Advances in semiconductor manufacturing processes have made possible the monolithic integration of passive components with active devices in a semiconductor substrate. For example, microelectromechanical systems (MEMS) devices can be connected with active circuitry for driving and/or signal processing of the MEMS devices through various vertical and lateral routing paths in an integrated semiconductor structure. Typically, the passive components, such as MEMS devices, are formed by using a layer-by-layer process over a semiconductor substrate during a back end of line (BEOL) processing after the active devices have been formed in the semiconductor substrate.
In a conventional process of monolithically integrating a MEMS device with active circuitry, a metal layer for forming a bottom electrode of the MEMS device is first formed over a semiconductor substrate, where the metal layer is connected to an active device in the semiconductor substrate through a routing path at the beginning of the fabrication process of the MEMS device. As the conventional process is carried out, the bottom electrode and other electrodes of the MEMS device are patterned using, for example, plasma etching. While the MEMS device is fabricated, however, heat and charge as results of thermal and plasma processes can build up and be transferred to the active device in the semiconductor substrate through the routing path. The heat and charge can adversely impact the performance of the active device as well as the MEMS device.
For example, in a monolithic integrated semiconductor structure formed by using the conventional process, a difference in performance has been observed between two MEMS devices, one connected to active circuitry and the other not. The difference in performance can be attributed in part to either a partial or total breakdown of an active device, such as a complementary-metal-oxide semiconductor (CMOS) transistor, in the active circuitry due to the heat and/or charge transfer. In addition, if too much charge is built up during the fabrication of the MEMS devices, the charge can cause damage to not only the active circuitry but also the MEMS devices.
Thus, there is a need in the art for a monolithic integration technique and structure for effective integration of passive components, such as MEMS devices, with active devices, such as CMOS transistors.